I've been playing guitar for about 2 years or so, on and off. I want to play another instrument so i figure bass would be the easiest to play as I already play guitar. I have some questions... do bassists generally have their fretting thumb over the neck or behind it? Would I be able to benefit from songwriting skills if I learned bass? How fast could I learn to play songs and could i be able to learn songs like crossroads or the lemon song in a couple months? Pick or no pick?